This invention relates to thermosetting emulsion latex mixtures and more particularly to an aqueous polymeric mixture containing polyol, an emulsion polymer, and a glycoluril adapted to be coreactive with the reactive emulsion polymer upon moderate heating. The thermosetting compositions are useful as wood coatings.
Glycoluril compositions are known for use in solvent based coatings such as disclosed in U.S. Pat. No. 4,064,191. Powder coatings based on glycoluril are disclosed in U.S. Pat. No. 4,118,432, U.S. Pat. No. 4,254,235 and U.S. Pat. No. 4,255,558. Low temperature cure aqueous dispersed coatings are disclosed in U.S. Pat. No. 4,442,257.
It now has been found that aqueous coatings based on glycoluril and emulsion polymers can be substantially improved by the inclusion of a polyol having a hydroxyl functionality of two and preferably three or more hydroxyl groups. The inclusion of polyol substantially improves stability of the aqueous dispersed glycoluril polymers and reactive emulsion polymers. Glycoluril-formaldehyde coatings can be formulated in accordance with this invention to provide highly crosslinked binders and coatings exhibiting excellent film properties. Emulsion polymers preferably containing reactive acrylamide, hydroxyl, or carboxyl groups can be blended with polyols and glycolurils such as methylolated glycolurils to produce high quality coatings which advantageously overcome excess formaldehyde emission problems typically associated with conventional phenol-formaldehyde or ureaformaldehyde systems. A further advantage of the inclusion of polyol in the thermosetting glycoluril and emulsion polymer mixtures is that the quantity of glycoluril can be substantially reduced while still maintaining equivalent or improved film properties. Lower raw material costs at lower crosslinker levels can be obtained in coating compositions prepared at higher solids content while substantially improving the stability of the aqueous dispersed polymeric mixture. A further advantage is achieved with respect to coalescent aids, which can impart water sensitivity to the coating, are no longer required. The coating compositions of this invention will cure as thermoset coatings on a substrate at low temperatures of about 40.degree. C. to 120.degree. C. at time intervals between 0.1 to 20 minutes and advantageously in less than three minutes. These and other advantages of the invention will become more apparent by referring to the detailed description and the illustrative examples.